The present disclosure relates generally to techniques for performing wellsite operations. More specifically, the present disclosure relates to techniques and apparatus for preventing blowouts, particularly in cold environments.
Oilfield operations may be performed to locate and gather valuable subsurface fluids. Oil rigs are positioned at wellsites, and downhole tools, such as drilling tools, can be deployed into the ground (via, for example, wireline or coiled tubing) to reach subsurface reservoirs. Once the downhole tools form a wellbore to reach a desired reservoir, casings may be cemented into place within the wellbore, and the wellbore completed to initiate production of subsurface fluids from the reservoir. Downhole tubular devices may be positioned in the wellbore to enable the passage of subsurface fluids to the surface.
Leakage of subsurface fluids may pose an environmental threat if released from the wellbore. Equipment, such as blowout preventers (BOPs), may be positioned about the wellbore to form a seal and to prevent leakage of subsurface fluids to the surface. BOPs may have selectively actuatable rams or ram bonnets, such as pipe rams or shear rams that may be activated to seal about the downhole tools or tubular devices and/or to sever these downhole tools or tubular devices, thereby insuring complete sealing of the wellbore.
BOPs must operate in a timely manner over a wide range of ambient temperatures to function as a safety device at full performance, including at sub-freezing temperatures (i.e., below water freezing temperatures) in land based wellsites. In particular, the fluid for hydraulically actuating the rams of a BOP may become increasingly more viscous at lower temperatures; this increased viscosity may cause a reduction of rate of flow to, and from, the rams of the BOP; and the BOP may become slow and dangerously less responsive.
Solutions to BOP operation in cold temperatures have, to date, been cumbersome low technology, in the form of heaters, insulators, circulating warming fluid, portable mountable BOP systems, using specialized fluids, or heating the hydraulic fluid itself, each of which is expensive and/or impractical for real application. Thus, there is a continuing need in the art for methods and apparatus for improved time responsiveness of blowout preventers, for example when temperature conditions make the fluid used to actuate the blowout preventers very viscous.